His design had a threaded barrel. Im guessing it was bean counters and politicains that made it a stamped, pinned & riveted ugly monster it is today LOL.

Im hoping to thread a trunion this week to get a idea of how hard its really going to be. i ahve made up alignment guagesa nd go no go guages and am working on a way to turn my mills spindle by hand with a tap in it. I spent yesterday cutting out blanks form 4130 plate and designing a G3 mag well and working on ways to keep the mag in. I have a super cool idea. Ill may be doing some extral long in the front bent blanks inthe near future that might be for sale if there is intreast. I also have the metal bent for the rails so the ejector wont have to be welded in on a standard rail.

My lathe is a 1950s Atlas 10x60. The Atlas design doubles the leadscrew as the power feed screw. It hangs right out in the open, for rust and swarf. By the time I got the lathe the screw was noticeably worn; despite my best attempts to preserve it, it's now worn to almost a V thread.

I could thread something long enough to hold in the steady rest, over an unworn portion of the screw, but it's all enough of a hassle I'd as soon avoid it.

So, I'd ordered a nice Romy underfolder flat from AK-Builder for $30, and a couple of Tapco flats from DPH for $15 each. I pulled the Tapco flats out of their bags and the outer sides have a very coarse belt-sanded finish, not at all like the one I bought a year ago.

So I set the first one up to bend... and bent it wrong.

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The top rails weren't completely bent at the front, and I'd measured across the outside. That made the sides .020" different in height.

My fault for not triple-checking. I measured to the inside of the (partial) bend on the second one, and got it right.

The AK-Builder flat, by comparison, is a whole different thing. Nice and smooth. No locating pin holes, so I had to drive my roll pins down flush. Stepped top rail! And properly bent and trimmed up front, no Dremel work needed to get the flat to fit into the slots in the trunnion. Beveled sides at the ejection area.

AK-Builder's equivalent (non underfolder) flat is $20. Next time I'll pay the extra $5, even if they don't come with lower rails.

I set the barrel up with the breech at the tailstock end so I could turn the threads down. There's a radius on the end of the tool to prevent a stress riser at the end of the cut.

Flip the barrel over, cut the step for the RSB. There was no way the Romanian bits were going to work, but the Chinese bits were all bigger. I only had to turn .020 or so off the barrel for the RSB.

Moving up to the handguard retainer area, I discovered the barrel wasn't straight, though it looked okay sighting down the bore. It was also out-of-round. The kicker is, it appeared to be rolled and welded, like muffler pipe! There was a dark line on the inside that I thought might have been rust from condensation. There's a definite lump on the outside, though, and you can see some imperfections where it was welded. I know Ford uses welded brake lines in their cars, and welded tubing does fine for hydraulic cylinders, and the .410 isn't a high pressure cartridge, but it was a bit creepy just the same.

The handguard retainer bit cleared up. I repositioned the barrel to reduce the unsupported area. When I bought the lathe, it came with TWO steady rests. Unfortunately, I just discovered one is apparently for a South Bend, or at least a 10" lathe with a single pyramidal way. The other fits the Atlas, but it's for a 12" lathe. <sigh> I sharpened the tool and made teeny tiny cuts, holding onto the barrel with my hand to damp the vibration.

Unfortunately the combination of warp and out-of-round on the gas block area made it impossible to turn concentric. After cogitating a while, I dressed the high spots with a file, then filed it down to the right size. It's a bit out of round, but it shouldn't affect the press fit.

I'll have to cut the barrel for the FSB later.

Fortunately, the Chinese parts were almost perfect. Even opening up the Romanian RSB and GB as far as they would go, I don't think I would have had enough barrel thickness to be safe. It would have required custom parts, or cutting and welding tubes to the Romanian parts.